Mel Gibson as a Bangkok tattoo artist in “The Hangover 2″? Hell, it could have been the celebrity cameo of the year.

Except now it won’t be.

Despite previous rumors that the cameo would definitely happen (and from all reports, it looked like it was a done deal), it now appears the displeasure of one Zach Galifianakis with said cameo has caused the studio and director Todd Phillips to “rethink” things.

I thought Mel would have been great in the movie and I had the full backing of [WB president] Jeff Robinov and his team. But I realize filmmaking is a collaborative effort, and this decision ultimately did not have the full support of my entire cast and crew.

Zach Galifianakis has made it pretty clear that he doesn’t approve of Gibson’s cameo in the movie, and recently told Comedy Death-Ray podcast host Scott Aukerman as much:

But a movie you’re acting in, you don’t have a lot of control — you just show up and vomit your lines out. I’m not the boss. I’m in a deep protest right now with a movie I’m working on, up in arms about something. But I can’t get the guys to [listen] … I’m not making any leeway.

Apparently you made plenty of leeway, Zach old chum.

Which begs the question: was Zach Galifianakis in similar “deep protest” over rapist Mike Tyson’s cameo in the first movie and simply not have the power to say No back then? One wonders…